Licona, Michael R. Why Are There Differences in the Gospels?: What We Can Learn from Ancient Biography. Oxford University Press. Kindle Edition.

Summarising the Introduction:

Any careful reader of the Gospels will notice that, despite many similarities, there are also differences between them.

Differences in parallel accounts can also be found in the secular biographies of the day: works by Tacitus, Suetonius, Plutarch, etc.

Various explanations of these differences have been offered: memory lapse, use of different sources, elasticity of oral tradition, flexibile nature of the biography genre, redaction, selectivity between different sources or authors, use of idioms that are unfamiliar to us, altering of sources to make a story seem more plausible.

In addition, we need to consider the norms that pertain to ancient compositional devices.  A study of how Plutarch reported the same events in nine of his Lives will demonstrate close similarities to the types of differences we see in the canonical Gospels.

While there are few if any parallels with Jewish literature, there are many similarities between the Gospels and Greco-Roman biography.

1.  They are written in continuous prose narrative.
2.  Stories, logia, anecdotes, and speeches are combined to form a narrative.
3.  The life of the main character is not always covered in chronological sequence.
4.  Attention is focused on a main character rather than on an era, event, or government as in a history.
5.  Little to no attention is provided for psychological analyses of the main character.
6.  We learn something of the main character’s ancestry and then move rapidly along to the inauguration of his public life.
7.  Ancient biographies were of the same general length, with shorter works being under 10,000 words, medium length between 10,000 and 25,000 words, and longer length over 25,000 words. Because a scroll would normally hold a maximum of 25,000 words, most biographies fell in the medium length category so they could be read in a single sitting.
8. 25 to 33 percent of the verbs are “dominated by the subject, while another 15 to 30 percent occur in sayings, speeches or quotations from the person.”
9.  Lives of philosophers and teachers are usually “arranged topically around collections of material to display their ideas and teachings.”
10. ​The main subject’s character is illuminated through his words and deeds as a model for readers either to emulate or to avoid.

On the other hand, there are profound differences between the Gospels and Greco-Roman biography, on the one hand, and modern biography, on the other hand.  In the former, authors felt at liberty to adapt details in order to bring out the the qualities of the main character.  In this regard, they were like modern movies that are ‘based on true events’.